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authorQian Cai <cai@lca.pw>2020-06-01 21:48:40 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-02 10:59:08 -0700
commitd6c1f098f2a7ba62627c9bc17cda28f534ef9e4a (patch)
tree1af69e6f983385bb0618fb2d2e03e2a60656322d
parent213516ac0752144ad1c82a0f8393f805c8abbc76 (diff)
mm/swap_state: fix a data race in swapin_nr_pages
"prev_offset" is a static variable in swapin_nr_pages() that can be accessed concurrently with only mmap_sem held in read mode as noticed by KCSAN, BUG: KCSAN: data-race in swap_cluster_readahead / swap_cluster_readahead write to 0xffffffff92763830 of 8 bytes by task 14795 on cpu 17: swap_cluster_readahead+0x2a6/0x5e0 swapin_readahead+0x92/0x8dc do_swap_page+0x49b/0xf20 __handle_mm_fault+0xcfb/0xd70 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x715 page_fault+0x34/0x40 1 lock held by (dnf)/14795: #0: ffff897bd2e98858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715 do_user_addr_fault at arch/x86/mm/fault.c:1405 (inlined by) do_page_fault at arch/x86/mm/fault.c:1535 irq event stamp: 83493 count_memcg_event_mm+0x1a6/0x270 count_memcg_event_mm+0x119/0x270 __do_softirq+0x365/0x589 irq_exit+0xa2/0xc0 read to 0xffffffff92763830 of 8 bytes by task 1 on cpu 22: swap_cluster_readahead+0xfd/0x5e0 swapin_readahead+0x92/0x8dc do_swap_page+0x49b/0xf20 __handle_mm_fault+0xcfb/0xd70 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x715 page_fault+0x34/0x40 1 lock held by systemd/1: #0: ffff897c38f14858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715 irq event stamp: 43530289 count_memcg_event_mm+0x1a6/0x270 count_memcg_event_mm+0x119/0x270 __do_softirq+0x365/0x589 irq_exit+0xa2/0xc0 Signed-off-by: Qian Cai <cai@lca.pw> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Marco Elver <elver@google.com> Cc: Hugh Dickins <hughd@google.com> Link: http://lkml.kernel.org/r/20200402213748.2237-1-cai@lca.pw Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/swap_state.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index ebed37bbf7a3..8238954ae781 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -509,10 +509,11 @@ static unsigned long swapin_nr_pages(unsigned long offset)
return 1;
hits = atomic_xchg(&swapin_readahead_hits, 0);
- pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages,
+ pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
+ max_pages,
atomic_read(&last_readahead_pages));
if (!hits)
- prev_offset = offset;
+ WRITE_ONCE(prev_offset, offset);
atomic_set(&last_readahead_pages, pages);
return pages;